Wonder why not.
Easy. If they had called anyone from RealNetworks, then under cross examination, Apple could have brought out that RealNetworks had hacked into the iPod to insert their DRM into the iPod's operating system. The Attorney Plaintiffs could not have that, because is destroys their case.
All Apple has to show is that Apple's changes to the iPod OS was to CLOSE VULNERABILITIES that could be used by hackers! If RealNetwork used a vulnerability that could have been used by them to insert their own version of DRM, it could a priori, be used by another hacker to insert code to steal music.
Apple can also show that the new OS changed features as well. . . adding more functionality to iTunes and iPod. There were major changes to the UI and abilities in iTunes 7.0 and iTunes 7.4 that are the upgrades that are being challenged in this case. For example iTunes 7.0 added September 12, 2006:
Video playback/purchasing improvements, iPod games, Major GUI changes, gapless playback and album, sync purchased content from iPod to computer, Cover Flow added.
And here's a biggie in 7.4, released September 7, 2007:
Support for iPod Touch, Classic (6G), Nano (3G), and adds interface art for new iPod Shuffle colors. GUI improvements.
You read that right. . . iPod touch! Apple added support in 7.4, the iPod touch screen. And these bozos claim it was ONLY about changing the OS to block RealNetwork! The most important and biggest change in the iPod is just not there. . .